THIS INVENTION relates to buried hetero-structure opto-electronic devices, and in particular to buried hetero-structure semiconductor lasers.
Buried hetero-structure semiconductor lasers have become widely-used in recent years as laser sources for, for example, optical communication systems. In a conventional buried hetero-structure semiconductor laser, an active layer (i.e. the layer in which the photons constituting the laser are actually generated) of a semiconductor material is buried within a larger bandgap semiconductor material. Semiconductor layers surrounding the active layer are grown to create a reverse biased junction, the active layer being positioned in a gap in the reverse biased junction. In operation of the device, electrical current flows across the semiconductor layers, substantially perpendicularly thereto. The reverse biased junction provides resistance to this, and the flow of current is directed through the gap in the reverse-biased junction, and hence through the active layer.
This structure does, however, suffer from drawbacks, in that, under high temperature and high output power operation, the flow of current across the device can be sufficient to drive electrons across the reversed biased junction, thereby drastically reducing the effectiveness of the device.
A further drawback of the above-described semiconductor laser is that the conventional fabrication process of such a device is rather complicated, as sufficient layers of appropriately doped semiconductor material to create a p-n-p-n thyristor must be grown in the correct order during manufacture of the device.
It is an object of the present invention to seek to alleviate some or all of these disadvantages.
Accordingly, one aspect of the present invention provide a method of manufacturing a semiconductor optical device comprising the steps of:
providing a substrate having an active layer thereon; providing an aluminium-bearing layer, the aluminium bearing layer being adjacent the active layer; and oxidising the aluminium-bearing layer substantially entirely.
Advantageously, the method further comprises the step of providing a mesa on the substrate and wherein the step of providing an active layer comprises the step of providing an active layer on the mesa.
Preferably, the step of providing a mesa on the substrate comprises the steps of: providing a substrate; and wet etching the substrate to form a mesa.
Conveniently, the step of providing a mesa on the substrate comprises the steps of: providing a substrate; and reactive ion etching the substrate to form a mesa.
Advantageously, the method further comprises the step of etching at least one groove in the device to a depth at least equal to that of the aluminium-bearing layer.
Preferably, the step of etching at least one groove in the device comprises the steps of: providing an etching mask an upper surface of the device, the etching mask having an elongate gap therein; and applying an etching process to the device.
Conveniently, the method further comprises the step of providing at least one further groove in the device, the at least one further groove being substantially parallel to the first groove.
Advantageously, the method further comprises the step of providing a cladding layer on top of the active layer or the aluminium-bearing layer.
Preferably, the method further comprises the step of providing a contact layer on the uppermost layer of the device.
Conveniently, the method further comprises the step of providing a first electrode on the device.
Advantageously, the method further comprises the step of providing a second electrode on an opposite side of the device from the first electrode.
Preferably, the step of providing an aluminium-bearing layer or the step of providing an active layer comprises the step of growth by a low pressure metal-organic vapour phase epitaxial technique.
Conveniently, the method further comprises the step of depositing a dielectric film on a layer of the device.
Advantageously, the step of depositing a dielectric film comprises the step of deposition by a plasma chemical vapour deposition method.
Preferably, the step of oxidising the aluminium-bearing layer substantially entirely comprises the step of heating the device in water-containing environment at a temperature of about 350 to 550xc2x0 C.
Conveniently, the water-containing environment is generated by the flow of a gas through water heated to about 80 to 90xc2x0 C. for about half an hour to about 10 hours.
A further aspect of the present invention provides a semiconductor optical device comprising: a substrate having an active layer formed thereon; and an aluminium-bearing layer, wherein the aluminium-bearing layer is adjacent the active layer and is oxidised substantially entirely.
Advantageously, a mesa is formed on the substrate, the active layer being located on the mesa.
Preferably, the device further comprises first and second electrodes on opposing sides thereof.
Conveniently, the device further comprises a cladding layer provided on the active layer or the aluminium-bearing layer.
Advantageously, the aluminium-bearing layer is substantially continuous apart from the region of the substrate on which the active layer is formed, thereby allowing electric current to flow from a first side of the device to a second side of the device only through the active layer.